Molecular characterization and identification of biocontrol isolates of Trichoderma spp.

The most common biological control agents (BCAs) of the genus Trichoderma h ave been reported to be strains of Trichoderma virens, T. harzianum, and T. viride. Since Trichoderma BCAs use different mechanisms of biocontrol, it is very important to explore the synergistic effects expressed by different genotypes for their practical use in agriculture. Characterization of 16 b iocontrol strains, previously identified as "Trichoderma harzianum" Rifai a nd one biocontrol strain recognized as T. viride, was carried out using sev eral molecular techniques. A certain degree of polymorphism was detected in hybridizations using a probe of mitochondrial DNA. Sequencing of internal transcribed spacers 1 and 2 (ITS1 and ITS2) revealed three different ITS le ngths and four different sequence types. Phylogenetic analysis based on ITS 1 sequences, including type strains of different species, clustered the 17 biocontrol strains into four groups: T. harzianum-T. inhamatum complex, T. longibrachiatum, T. asperellrrm, and T. atroviride-T. koningii complex. ITS 2 sequences were also useful for locating the biocontrol strains in T. atro viride within the complex T. atroviride-T: koningii. None of the biocontrol strains studied corresponded to biotypes Th2 or Th4 of T. harzianum, which cause mushroom green mold. Correlation between different genotypes and pot ential biocontrol activity was studied under dual culturing of 17 BCAs in t he presence of the phytopathogenic fungi Phoma betae, Rosellinia necatrix, Botrytis cinerea, and Fusarium oxysporum f. sp. dianthi in three different media.